rtl8139 driver patch

[Marty Connor <mdc@thinguin.org>]

On 12/23/1999 5:46 AM ken@nlc.net.au Ken Yap wrote:
>Rainer who wrote the driver is probably not on the list, but I asked
>myself this question once. I looked at the data sheet, and it appears
>you cannot configure fewer than 4. If you can get it to work with less,
>please do.

This had been bothering me as well.  I ran the following command to check 
driver sizes:

    # size *.tmp | sort -r -k4,4
       text        data     bss     dec     hex filename
      11428         368   17753   29549    736d smc1211.tmp
      11428         368   17753   29549    736d rtl8139.tmp
      11241         312   12537   24090    5e1a tulip.tmp
      11355         344   11609   23308    5b0c ntulip.tmp
      11355         344   11609   23308    5b0c mx987x5.tmp
      11355         344   11609   23308    5b0c lc82c115.tmp
      11127         248    6560   17935    460f epic100.tmp
      11063         344    6489   17896    45e8 lancepci.tmp
      12151         316    5188   17655    44f7 eepro100.tmp
      13831         404    3417   17652    44f4 3c90x.tmp
       9027         282    6457   15766    3d96 ne2100.tmp
       9008         282    6457   15747    3d83 ni6510.tmp
      11670         202    3353   15225    3b79 cs89x0.tmp
      11383         340    3385   15108    3b04 nepci.tmp
       9997         318    3321   13636    3544 smc9000.tmp
       9864         205    3353   13422    346e 3c509.tmp
       9686         304    3353   13343    341f wd.tmp
       8823         828    3353   13004    32cc exos205.tmp
       9304         202    3417   12923    327b sk_g16.tmp
       9290         214    3353   12857    3239 ne.tmp
       8838         512    3353   12703    319f ni5210.tmp
       8949         354    3353   12656    3170 3c507.tmp
       8976         202    3353   12531    30f3 3c503.tmp
       7969         234    3353   11556    2d24 tiara.tmp

I noted that the driver size for the rtl8139 driver was, as suspected 
quite high.  I looked at the source (rtl8139.c) and noticed that the 
transmit buffer was being allocated for 4 buffers.  I also noticed that 
the Etherboot system is polling, and is a single-threaded architecture. 

I then downloaded the rtl8139A data sheet from the RealTEK site, and 
found that although there are 4 available transmit descriptors, there is 
no requirement that there be 4 seperate buffers for them, since if we are 
in full control of transmission we can be sure that only one packet is 
put in the buffer at a time. 

I made the following changes to rtl8139.c:

   120c120
    <       unsigned char tx_bufs[TX_BUF_SIZE * NUM_TX_DESC + 4];
    ---
    >       unsigned char tx_bufs[TX_BUF_SIZE + 4];
    302c302
    <               tx_buf[i] = my.tx_bufs + i*TX_BUF_SIZE;
    ---
    >               tx_buf[i] = my.tx_bufs;

With the following results:

before:
       text        data     bss     dec     hex filename
      11428         368   17753   29549    736d rtl8139.tmp
after:
       text        data     bss     dec     hex filename
      11428         368   13145   24941    616d rtl8139.tmp

There is a resulting savings of about 4.5K bytes, which is a lot of space 
when all we have is 32K bytes to play with.  The driver seems to function 
identically, since basically, I just pointed all of its transmit 
descriptors at the same buffer, and made sure that only one transmit 
event was requested at a time.

Perhaps this change will help people who are having problems with this 
driver that may be related to memory corruption above 32K, by allowing 
more room for stack growth.  There are a few other things that can be 
done, but this is the easiest way to save memory, so let's try this first.

Those who can, please test the above 2 line patch and see if it helps fix 
problems.

Regards,

Marty

---
   Name: Martin D. Connor
US Mail: Entity Cyber, Inc.; P.O. Box 391827; Cambridge, MA 02139; USA
  Voice: (617) 491-6935, Fax: (617) 491-7046 
  Email: mdc@thinguin.org
    Web: http://www.thinguin.org/


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